The relative changes are very small, and could hardly account for the divergence of the male and female intrinsic rates. The new fathers are not sufficiently young in relation to the age of their wives to explain the much higher current male intrinsic rate.
In fact, the explanation is in the male age distribution as a whole rather than in ages of fathers as such. Because the fathers of the mid-1960's are the births of the 1940's and during the 1940's the births were rising rapidly, we now suddenly have a much steeper decline with age of the number of young men and women than usual: The age distribution has an especially sharp fall from 20 to 30. If women are paired with men on the average 3 years older, then an increase in both men and women of the same ages increases the number of women in the denominator of the age-specific rates more than it increases the number of men. The denominator for women is diluted, so to speak, with women who in the current configuration of ages of husbands and wives cannot have spouses with the usual age difference. This increase of the denominator for women lowers their age-specific rates, and hence the Net Reproduction Rate RQ and the intrinsic rate r.
The marriage market is constituted by the numbers of males and females of corresponding ages. What are corresponding ages in the United States in 1967 is suggested by the median groom at first marriage being 23.1 years old and the median bride being 20.6 years old, a difference of 2.5 years. The mean age of fathers in the stationary population in 1966 was 29.33, and of mothers in the same year was 26.35, a difference of nearly 3 years.
The numbers at youthful ages in the United States in 1966 were
Males
Females
10-14 15-19 20-24 25-29 30-34
To compare the women of one age group with the men of the group 5 years older exaggerates the discrepancy but will serve us as an index. We can see from the above data that the biggest disproportion in 1966 is between the women 15 to 19 and the men 20 to 24; as these come to marriage age, which is just about now, the shortage of men will be more serious than 5 years earlier or 5 years later. (Allowance for military personnel stationed outside the United States—omitted from the above official estimates—would somewhat reduce the effect under discussion.)
Japan shows the same phenomenon in its 1966 age distribution:1966 29.33 26.35 diagram may help us follow the preceding arguments.